1. Field of the Invention
The invention relates to an insulated wire and a coil using the insulated wire.
2. Description of the Related Art
Electric equipment, in which a coil formed by welding and bonding the end portions of insulated wires is used, are desired to be small and to be driven at high voltage so as to improve the performance. Therefore, there is a tendency that electric equipments are inverter-controlled at higher voltage than before and a value of inverter surge voltage generated by the inverter control thus rises, which results in that the insulated wires are used under an environment in which partial discharge is more likely to occur than before.
Thus, in recent years, the insulated wires are desired to have a higher partial discharge inception voltage than a conventional insulated wire so as to suppress the occurrence of partial discharge caused by an increase in inverter surge voltage.
An insulated wire with a high partial discharge inception voltage is known in which plural layers of insulating covering films made of a specific material are formed on a conductor (see, e.g., JP-A-2011-165485). Here, the plural layers of insulating covering films include first and second covering film layers. The first covering film layer is formed of a first resin composition formed by graft-polymerizing a graft compound onto an ethylene-tetrafluoroethylene copolymer and the second covering film layer is formed of a second resin composition as a polymer alloy composed of a polyphenylene sulfide resin and a polyamide resin.
JP-A-2011-165485 discloses that excellent abrasion resistance and heat resistance of the second resin composition constituting the second coating layer can be obtained when a storage elastic modulus at 20° C. is not less than 1 GPa and a storage elastic modulus at 200° C. is not less than 10 MPa.